<PRE><B>Question 263757</B>
Translate the problem into a pair of linear equations in two variables.Solve the equations using either elimination or substitution.

Problem:
A contractor mixes concrete from bags of pre-mix for small jobs. How many bags with 7% cement should he mix with 10 bags of 15.5% cement to produce a mix containing 12% cement? 

let the total no of bags be x

then x-10 will be number of bags with 7% cement

x-10*0.07+0.155*10= x*0.12

0.07x- 0.7+1.55=0.12x
-0.05x =-0.85
x= 17 bags

7 bags of 7% cement will have to be mixed

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